ABSTRACT
The May 12, 2008 Great Wenchuan Earthquake has resulted in more than 69,227 deaths, 17,923 missing, 374,643 injured (up to September 22, 2008), and at least 4.8 million people became homeless. Unofficial estimation of total economic loss may be as high as US$75 billion dollars. A total of 391 dams were damaged by the earthquake, but luckily no failure of dam was reported. It occurred at about 14:28:01 pm local time and China Earthquake Administration estimated the surface magnitude is 8.0 whereas the moment magnitude is 7.9 (assigned by USGS). However, some Chinese seismologists estimated the moment magnitude may be as high as 8.3 based on seismic moment calibrated from seismic stations all over the world. The ground shaking lasted for about 3 minutes, depending on the distance from the fault zone. The peak ground acceleration (PGA) recorded at various seismic stations had been exceeding or close to 1g (i.e. 9.81 m/s2). It was believed that at the epicentral areas, the PGA is much larger than 1g. Aftershocks continued to shake the area months after the earthquake, eight of them exceeding a magnitude of 6.0. The largest one was magnitude 6.4 on May 25, 2009 when the author had just finished his first excursion to Sichuan. The maximum slip on the fault surface was estimated from 9 m to 15 m with an average of exceeding 2 m, that seems agree with the slip deformation observed at surface ruptures (maximum vertical and horizontal displacement are 6.5 m and 4.9 m respectively) (Xu et al. 2008).
